In the drilling of offshore petroleum or gas producing wells from a fixed platform it is customary to insert a conductor member into the marine structure between the work deck and the wellhead. This conductor serves the primary purpose of enclosing the rotating drill string. Thus, drilling mud can be circulated through the drill string and returned to the pumps on the working deck.
In some instances where the petroleum-bearing reservoir is determined to be relatively close to the surface of the water, it is necessary to offset the rotating drill string rather quickly so it will assume a desired direction whereby to enter the reservoir. In shallow areas this offsetting of the drill string from vertical must be accomplished as soon as possible so that the drill will intersect the reservoir within a short period of time.
It is known that by initially deflecting the drill string such that it enters the ocean floor at a desired angle, the operation is expedited. In one method of achieving such directional drilling, the conductor is positioned within the offshore structure and initially aligned at an angle to the structure floor. Thus, the drill string, by being guided through the conductor, will enter the floor at a predetermined angle and direction.
It is also known that to effectuate the desired offset, the drill string can be initially forced from a vertical disposition into the desired entry angle. This is normally done through use of an elongated conductor guide which is carried within the body of a marine platform.
The guide comprises a heavy walled tube-like member which is performed into a desired curved configuration, limited by the drill string's bending capability. The addition of curved or straight guide members to the underwater section of a marine structure after it has been placed at an offshore site is usually an expensive operation requiring the use of divers and other special equipment.
The instant invention therefore provides a novel method for utilizing an offshore structure, which permits a directional drilling of well bores. The method further serves to reduce overall operating expenses and provides the structure with a greater degree of versatility due to the greater number of wells that can be drilled from a single site. The method further permits ready positioning of drill conductor guides by suspending a drill conductor guide cage outboard of the structure.
The marine structure presently contemplated for practicing the method is provided with ordinary drilling equipment such as derrick, rotary table and the like. However the platform is also provided with an elongated cage or substructure which serves as an underwater support member for one or more conductor guides.
The cage is built such that it can be detached from its normal submerged position in the marine structure, and raised to the working deck. The cage is further provided with means for pivotally swinging the entire unit outboard of the working deck and into a substantially horizontal position thereby facilitating its being worked on.
Thus, the number of, or the pattern of conductor guides can be changed by addition to, or removal of said guides to achieve a desired pattern at the ocean floor. The cage thereafter can be swung back on board the platform and into a vertical position prior to being reinserted by lowering into its normal seating or working position. Thus, the original conductor guides, or the newly inserted guides, are so aligned to permit further drilling in a particular direction from an initially upright disposition of the drill string.
It is therefore an object of the invention to provide a method to facilitate deviated drilling at an offshore site. A further object is to provide a method for drilling a plurality of well bores from a single offshore drilling platform.